MD_DataIdentification

TerraPoint surveyed and created this data for the Puget Sound LiDAR Consortium under
contract. The area surveyed is approximately 100 square miles and covers part of Lewis
County, WA. All data was collected during ideal conditions (leaf-off). The LAS files
were derived from all returns ASCII files contain the X,Y,Z values of all the LiDAR
returns collected during the survey mission. The GPS time, classification, scan angle,
intensity and return numbers of each point were preserved in the conversion from ASCII
to LAS. The LAS files are classified into the following ASPRS classes: (1) Unclassified
(2) Bare Earth. Ground and water points are included in Class 2 (Bare Earth). Futher
details are available in the Process Steps below. The NOAA Coastal Services Center
noticed that some intensity values are 0, so be aware before using the intensity information.
This dataset was flown in 2003 with a 50% overlap between flight lines. Due to the
overlap the nominal point spacing of the dataset is 1.0 meter.

These data depict the elevations at the time of the survey and are only accurate for
that time. Users should be aware that temporal changes may have occurred
since this data set was collected and some parts of this data may no longer represent
actual surface conditions. Users should not use this data for critical
applications without a full awareness of its limitations. Any conclusions drawn
from analysis of this information are not the responsibility of NOAA or any of its
partners. These data are NOT to be used for navigational purposes.

Acquisition. Lidar data were collected in leaf-off conditions (approximately 1 November
- 1 April) from a fixed-wing aircraft flying at a nominal height of 1,000 meters above
ground surface. Aircraft position was monitored by differential GPS, using a ground
station tied into the local geodetic framework. Aircraft orientation was monitored
by an inertial measurement unit. Scan angle and distance to target were measured with
a scanning laser rangefinder. Scanning was via a rotating 12-facet pyramidal mirror;
the laser was pulsed at 30+ KHz, and for most missions the laser was defocussed to
illuminate a 0.9m-diameter spot on the ground. The rangefinder recorded up to 4 returns
per pulse. Flying height and airspeed were chosen to result in on-ground pulse spacing
of about 1.5 m in the along-swath and across-swath directions. Most areas were covered
by two swaths, resulting in a nominal pulse density of about 1 per square meter.

ASCII file generation All Point returns with all their attributes were directly exported
into ASCII files. These were first divided into USGS quarter quads (3.25 minute by
3.25 minute) and then in 25 tiles per quarter quad.

1

2013-02-01T00:00:00

The NOAA Coastal Services Center (CSC) received topographic files in ASCII .TXT format.
The files contained lidar elevation measurements. The data were received in Washington
State Plane South Zone 4602, NAD83 coordinates and were vertically referenced to NAVD88
using the Geoid99 model. The vertical units of the data were feet. CSC performed the
following processing for data storage and Digital Coast provisioning purposes: 1.
The ASCII .TXT files were parsed and converted to LAS version 1.2 using LAStools'
txt2las tool. 2. Bad elevation values were filtered and removed throughout the dataset
on a tile by tile basis using LASTools' las2las tool. 3. The topographic las files
were converted from orthometric (NAVD88) heights to ellipsoidal heights using Geoid99.
4. The topographic las files were converted from a Projected Coordinate System (WA
SP South) to a Geographic Coordinate system (NAD 83). 5. The topographic las files'
vertical units were converted from feet to meters. 6. The topographic las files' horizontal
units were converted from feet to decimal degrees. 7. The data were converted to LAZ
format.

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2013-04-25T00:00:00

The NOAA National Geophysical Data Center (NGDC) received lidar data files via ftp
transfer from the NOAA Coastal Services Center. The data are currently
being served via NOAA CSC Digital Coast at http://www.csc.noaa.gov/digitalcoast/.
The data can be used to re-populate the system. The data are archived in LAS or LAZ
format.
The LAS format is an industry standard for LiDAR data developed by the American Society
of Photogrammetry and Remote Sensing (ASPRS); LAZ is a loseless compressed version
of
LAS developed by Martin Isenburg (http://www.laszip.org/). The data are exclusively
in geographic coordinates (either NAD83 or ITRF94). The data are referenced vertically
to
the ellipsoid (either GRS80 or ITRF94), allowing for the ability to apply the most
up to date geoid model when transforming to orthometric heights.